Field of the Invention
The present invention relates to an image processing apparatus and method, which can add predetermined additional information to an input image so as not to be easily identified by human eyes, and a storage medium which stores a program for performing the method.
Related Background Art
In recent years, along with the improvement of performance of image recording apparatuses such as color printers, color copying machines, and the like, higher-quality images can be formed. Owing to this, it is becoming easy to form an image having nearly the same image quality as that of securities such as bank notes and the like.
In order to inhibit such illicit image formation, a method of determining the formation conditions of an image by decoding the formed image is known.
For example, a dot pattern that represents the machine number of an image recording apparatus may be hidden in a color image to be printed.
Since this dot pattern is hidden in a specific color component (yellow) of the color image, it is hardly identified by the human eyes. Hence, the printed image seems nearly the same as an original image.
On the other hand, a conventional image recording apparatus, which can print on both an OHT (a transparent film used in an OHP) and normal paper, can print in correspondence with the fixing characteristics of recording agents (toner, ink) for these recording media by changing the image formation process (the traveling speed of each recording medium).
However, the conventional apparatus always adds a dot pattern with a constant density irrespective of different image formation processes of the image forming means. For example, in the image formation process for the OHT, since the OHT travels at a low speed to allow easy fixing of the recording agent, the dot pattern which should have a constant density becomes unwantedly conspicuous. As a technique for solving this problem, the type of recording sheet is detected using, e.g., a sensor, and additional information is added by a method suitable for the detected recording sheet. However, the apparatus becomes expensive since it must additionally comprise the sensor.